Nutriments and fodders have heretofore been produced by propagating Candida yeasts on molasses. The yeast cells that are thus grown are separated from the resulting brew by centrifugation or conventional filtration and dried, and the dried product is used as animal fodder or fodder supplement. Candida yeast contains between 40 and 50% by weight of protein, dependent upon the strain and the conditions under which it was cultivated or grown.
The production of protein-containing animal fodders or fodder supplements by cultivation of yeasts and similar microorganisms on whey has also been described, for example, in U.S. Pat. No. 2,809,113. However in the process described in that patent, the brew is heated so as to release the cell substances of the yeast and the liquid that is then separated from the solids is concentrated and the concentrated solution is spray-dried.
Processes have also been described for fractionating or separating the soluble proteins that are present in whey by ultrafilters provided with membranes that are impermeable to the soluble proteins and thereafter the filtered whey from which the soluble proteins have thus been separated is used for cultivation of yeast to produce protein-containing animal fodders and fodder supplements. Such ultrafiltration processes are described in papers by Roualeyn I. Fenton-May and Charles G. Hill, Jr., and Clyde H. Amundson, entitled "Use of Ultrafiltration/Reverse Osmosis Systems for the Concentration and Fractionation of Whey" published in Journal of Food Science, volume 36, pages 14-21 (1971), and by I. K. Nielsen, A. G. Bundgaard, O. J. Olsen, and R. F. Madsen, entitled "Reverse Osmosis for Milk and Whey", published in Process Biochemistry, September 1972, pages 17-20. In such ultrafiltration processes the soluble proteins of whey become entrained in the membranes, thereby retarding or slowing and ultimately stopping the filtration.
Heretofore, in using whey as a medium for the propagation of yeasts, the cells of which are usually separated from the brew by means of centrifugal separators, the filtrate or waste water is generally contaminated with the soluble proteins or products thereof that are formed during the cultivation of the yeast. In order not to contaminate the environment, methods for the preliminary removal of the soluble proteins, such as the foregoing ultrafiltration processes, and subsequent removal of the salts by centrifugation, have been considered. Such treatment nonetheless are costly and uneconomical.